Multistage steam reheating



May 22, 1962 A. BRUNNER MULTISTAGE STEAM REHEATING 3 Sheets-Sheet 1Filed March 9. 1959 Fig. 4

T 777 YI'TY' INVENTOR. ALFRED BIPUIVNEIR ATTORNEX May 22, 1962 A.BRUNNER MULTISTAGE STEAM REHEATING 5 Sheets-Sheet 2 Filed March 9. 1959.E NN u ME 5 HTTO/PNEX May 22, 1962 A. BRUNNER MULTISTAGE STEAMREHEATING 3 Sheets-Sheet 3 Filed March 9. 1959 INVENTOR. ALFREDBRUNNEE'.

United States Patent ()7 3,035,556 MULTISTAGE STEAM REHEATIN G AlfredBrunner, Winterthur, Switzerland, assignor to Sulzer Freres, S.A.,Winterthur, Switzerland, :1 corporation of Switzerland Filed Mar. 9,1959, Ser. No. 798,039 Claims priority, application Switzerland Mar. 12,1958 1 Claim. (Cl. 122-476) The present invention relates to a methodfor influencing the condition of the steam leaving resuperheatersoperating at different pressures and associated with a live steamgenerating plant, and to an apparatus for practicing the method.

The method according to the invention includes the step of exchangingheat between the steam at the relatively hot end of one reheater and thesteam at the relatively cool end of another reheater.

In the apparatus for practicing the method according to the invention atleast one heat exchange surface is provided on one side of which flowssteam of the relatively hot end portion of one reheater and on the otherside of which flows steam of the relatively cool end portion of theother reheater.

An advantage of the method and apparatus according to the invention isthat the heat exchange surfaces of two reheaters operating at differentpressures and temperatures can be reduced almost one half of thatrequired for reheaters operating at the same steam temperatures butwithout heat exchange between the steams of the reheaters, because, withheat exchange between the steams of the reheaters, the steam of onereheater is cooled while the steam of the other reheater is heated orvice versa.

The apparatus according to the invention includes dis tributing valvesfor distributing the steam onto the heat exchange surface wherebyactuation of these valves does not change the sum of the enthalpies ofthe steam flowing on one side and of the steam flowing on the other sideof the heat exchange surface. Actuation of the steam distributingvalves, therefore does not cause a disturbance which may affect thecontrol of the heating apparatus of the steam generator with which thereheaters are associated.

The novel features which are considered characteristic of the inventionare set forth with particularity in the appended claim. The inventionitself, however, and additional objects and advantages thereof will bestbe understood from the following description of embodiments thereof whenread in connection with the accompanying drawing, in which:

FIG. 1 is a diagrammatic longitudinal sectional view of a combustion gasduct containing a two-stage reheater forced flow steam generatorincluding a further modi fication of a two-stage reheater arrangement.

FIG. is a diagrammatic vertical sectional view of a forced flow steamgenerator equipped with a two-stage reheater arrangement and includingautomatic controls, FIG. 5a showing detail of the latter.

FIG. 6 is a diagrammatic illustration of a two-stage reheater and heatexchanger arrangement and of control means therefor.

FIG. 7 is a diagrammatic illustration of a modification of the two-valvecontrol mechanism shown in FIG. 6.

3,035,556 Patented May 22, 1962 Referring more particularly to FIG. 1 ofthe drawing, steam leaving, for example, the high pressure stage of asteam power plant flows through a pipe 1 into one side of an indirectheat exchanger 2. Thereupon the steam passes through a first reheater 3into a pipe 4 which may be connected to the inlet of a medium pressureturbine, not shown. Low pressure steam, for example the exhaust of amedium pressure turbine, flows on the side of the heat exchange surfaceof the heat exchanger 2 which side is opposite to the side where themedium pressure steam flows.

The low pressure steam arrives through a pipe 5 and flows through themain part 6 of the second or low pressure reheater wherein the lowpressure steam is reheated. The relatively hot low pressure steam isconducted from the end of the reheater part 6 through a pipe 8 to adistributing valve 9 which may be automatically controlled by controlsignals received from a conductor 10. Such control will be describedlater. A pipe 11 connects the valve 9 to the low pressure steam inlet ofthe heat exchanger 2. A pipe 12 connects the low pressure steam outletof the heat exchanger 2 to an end section 7 of the low pressurereheater. A by-pass pipe 13 connects the valve 9 directly to the pipe12. The outlet of the low pressure reheater section 7 may be connectedby a pipe 14, for example, to a low pressure turbine. An arrow 15indicates the flow of combustion gas through a flue 16 in which thereheaters are placed. It makes no difference for the system according tothe invention whether the distributing valve 9 is connected to themedium pressure side of the heat exchanger 2, i.e. is interposed in thepipe, or is connected to the low pressure side as shown. It the valve 9is interposed in the pipe 1, the by-pass pipe must be connected to theinlet .of the reheater 3 and pipe 8 must be directly connected to thelow pressure side of the heat exchanger 2, in lieu of the pipe 11.

Since the heat exchanger 2 is arranged at the relative cool or inletportion of the medium pressure reheater 3, the medium pressure steam isheated and the low pressure steam is cooled. If the heat exchange 2 isconnected to the relatively hot end, i.e. to the outlet part, of thereheater 3, and steam is taken from the relatively cool part of thereheater 6, the medium pressure steam is cooled and the low pressuresteam is heated.

In the embodiment of the invention diagrammatically shown in FIG. 2 afirst reheater 17, 18 as well as a second reheater 21, 22 are providedwith heat exchangers 23 and 24, respectively, whereby the heat exchangerassociated with one of the reheaters is heated by steam from the otherreheater. The heating steam taken from the main parts 17 and 21 of thetwo reheaters is cooled in the respective heat exchanger. The heatexchangers 23 and 24 are located outside of the flue gas channel 25which is shown in cross section, the combustion gas flowing in adirection normal to the plane of the drawing as indicated by an arrow 26shown in end view. The two reheaters are placed in the same plane andfill the flue. The two reheaters can therefore be made alike so thatthey can be interchanged and it is sufiicient to have only one sparereheater.

If the heat supply to both reheaters is the same, the arrangementaccording to FIG. 2 has the advantage that the heating surfaces of thereheaters are small and can easily be arranged in boiler fines where thespace is limited.

Valves 27, 28 regulating the steam flow through the reheaters arepreferably automatically controlled as will be described later, wherebya control signal is conducted to actuating means for the valves througha conductor 29. The connection of the reheaters 17, 18 and 21, 22 to therespective heat exchangers is like the one shown in FIG. 1.

The medium pressure steam is supplied to one side of the heat exchanger23 through a pipe 1 and leaves the reheater 1'7, 18 through a pipe 4.The low pressure steam is conducted to the low pressure side of the heatexchanger 24 through a pipe and leaves the low pressure reheater througha pipe 14.

A control apparatus which will be described later supplies controlpulses through a conductor 29 to motor operators for the valves 27, 28which operate the valves in opposite senses. When the valve 27 openssteam passage to the heat exchanger 23 andcloses the by-pass to thereheater section 2 2, the valve 23 closes passage of steam through theheat exchanger 24 and opens the by-pass to the reheater section 18.-

The valves 27, 28 may be actuated simultaneously or consecutively. If,in the latter case, for example, the flow through both valves 27, 28 wascompletely stopped, the control apparatus would completely open onevalve before completely opening the second valve and vice versa. Thecontrol may be so arranged that opening of the valves is effectedconsecutively and closing is effected simultaneously or vice versa.

The reheater 31 shown in FIG. 3 has portions 32 and 33 wherein two tubesare coaxially placed one within the other. The entire reheater 31 withthe portions 32 and 33 is placed in a combustion gas duct 34 throughwhich the combustion gases flow in the direction indicated by arrow 35.Medium pressure steam is conducted through a pipe 1 into the outer tubeof the portion 32 wherefrom the steam consecutively passes through acentral portion of the reheater and through the outer tube of theportion 33 into a pipe 4.

The low pressure steam arrives through a pipe 5 in which a distributingvalve 36 is interposed which directs the low pressure steam eitherthrough a pipe 37 into the inner tube of the reheater and heat exchangerportion 33 and therefrom through a pipe 39 to the main part 41 of a lowpressure reheater 41, 42, or through a by-pass pipe 43 directly into thelow pressure reheater part 41.

The low pressure steam heated in the reheater part 41 flows through aconduit 44 to a valve 45 wherefrom the steam is directed through a pipe46 into the inner tube of the heat exchanger and reheater portion 32 andtherefrom through a pipe 48 into the end portion 42 of the low pressurereheater. The reheated low pressure steam is conducted through a pipe14, for example, to a low pressure turbine. A by-pass pipe 49 isprovided for by-passing the heat exchanger and reheater portion 32 andconnecting the valve 45 directly to the pipe 48.

In connection with heat exchangers consisting of tubes coaxially placedwithin each other and being heated also from the outside, it ispreferred to connect the distributing valves to the inner tubes so thatsteam flows at all times through the outer tubes preventing overheatingof the latter.

The distributing valves 36, 45 in FIG. 3 may be operated simultaneouslyor consecutively or the two operating methods may be combined, asdescribed in connection with FIG. 2.

The steam generator 51 shown in FIG. 4 includes a combustion chamber 52,gas ducts 53, 54 receiving hot combustion gas therefrom, and a flue 55for conducting the combustion gas into a stack, not shown. Thecornbustion chamber 52 is provided with a tilting burner 56 whoseposition is controlled by a motor operator 57 which responds to signalsin a conductor 58. This control will be described later. Combustion airis supplied by a blower 59 having an intake 60.

The walls of the combustion chamber 52 are lined by tubes forming anevaporator 61 which receives feedwater from a feed pipe 62. The steamleaving the evaporator 61 is dried in a water separator 63 and conductedinto a high pressure superheater having a first section 64 whose tubesline the walls of the upper part of the combustion chamber 52. Theevaporator 61 and the primary superheater 64 are exposed to radiant heatwhereas a secondary superheater portion 66, which is connected to theportion 64 by a pipe 65, and reheaters 67 to 69 are heated byconvection.

The outlet 92 of the second superheater portion may be connected to ahigh pressure turbine. A medium pressure primary reheater portion 68located at the outlet of the gas duct 54 receives medium pressure steamfrom a pipe 70. A second portion 67 of the medium pressure reheater isarranged upstream of the second high pressure superheater 66 withrespect to the flow of the combustion gases.

The outlet of the first portion 68 of the medium pressure reheater isprovided with a valve 71 whose motor operator is controlled by controlsignals arriving through a conductor 72 for selectively conducting steamthrough a pipe 73 to an inner tube 74 of the steam heat exchangerportion 75 of a low pressure reheater or through a bypass pipe 76 and apipe 77 directly into the second part 67 of the medium pressurereheater. The outlet 78 of the latter may be connected to a mediumpressure turbine, not shown.

Low pressure steam is supplied through a pipe 79 to the outer tube ofthe steam heat exchanger 75 wherefrom the low pressure steam flowsthrough a combustion gas heated portion 69 of the low pressure reheaterwhose outlet 30 may be connected to a low pressure turbine, not shown.

Placement of a reheater in the combustion gas stream between portions ofa reheater operating at a different pressure and temperature has theadvantage that the reheat temperature at the outlets of both reheaterschanges substantially to the same extent when the temperature of thecombustion gas changes. If the position of the tilting burner 56 ischanged, the heat transfer conditions in both reheaters are changedsubstantially in the same manner.

The condition of the steam at the outlet of the reheaters ischaracterized by its temperature, pressure, density, and moisturecontent. If the temperature of the steam at the outlets of the reheatersmust be maintained when the load is changed or the pressure of the steammust be changed for producing a desired load, heat exchange between thesteams of the reheaters is of advantage. For controlling,

' for example, the outlet temperatures of the reheaters, preferably thesum of the temperatures atthe reheater outlets is used as the controlledvariable for producing control pulses for manipulating one or acombination of the following variables: fuel supply, combustion airsupply, location of the heat center, feedwater supply. If the fuelsupply is controlled, the air supply will be controlled according to thefuel supply, and vice versa, in order to operate at a good combustionefiiciency.

In order to have the desired outlet temperature at each reheater, thedifference between the outlet temperatures is preferably used forcontrolling the heat exchange between the steams passing through thereheaters.

If the reheaters form part of a steam generator which producessuperheated high pressure steam which, after expansion, is reheated inthe reheater, and if it is desired to control the temperature of thesuperheated high pressure steam, a variable is preferably manipulatedwhich is not included in the above listed variables. In this case thecontrolled variable may be the amount of cooling water injected into thehigh pressure superheater.

FIG. 5 illustrates a steam generating system having two reheaters and asteam heat exchanger at the inlet of the low pressure reheater andheated by steam leaving a first section of a medium pressure reheater.Feedwater is heated in an economizer 103 located in a flue 104. Thewater is evaporated in an evaporator 106 located in a combustion chamber107 which is heated by a tilting burner 108. The wet steam produced inthe evaporator 106 is dried in a water separator 109 and superheated ina first superheater 110 arranged to receive heat by radiation in thecombustion chamber 107. The steam leaving the primary superheater 110 isfurther superheated in a second superheater 111 located in the flue 104.The steam leaving the second superheater flows through a live steam main112 to a high pressure turbine 113 whose exhaust is conducted through afirst medizm pressure reheater section 114 located in the combustionchamber 107. A pipe 115 conducts the medium pressure steam from thereheater section 114 to a heat exchanger 116 wherefrom the steam isconducted through a pipe 117 to a distributing valve 118 to which aby-pass pipe 119 and, through a pipe 121, a second medium pressurereheater section 122 are connected. The latter receives heat byconvection from the combustion gas produced in the combustion chamber107. The steam reheated in the section 122 flows through a pipe 123 to amedium pressure turbine 124.

The low pressure steam exhausting from the medium pressure turbine 124flows through a pipe 125 to the heat exchanger 116 and therefromconsecutively through three low pressure reheater sections 126, 127 and128. The reheated low pressure steam is conducted through a pipe 129 toa low pressure turbine 131.

A thermostat is connected to each of the pipes 123 and 129 for measuringthe temperature of the medium pressure and of the low pressure reheatedsteam. The thermostat connected to the pipe 123 includes a rod 144 of amaterial whose heat expansion coefficient is smaller than that of thepipe 123. One end of the rod 141 is pivotally connected to the pipe 123at 136. The second end of the rod 141 forms the fulcrum of a lever 138one arm of which is pivotally connected to the pipe 123, the second armof the lever 138 actuating a piston valve 145 through a spring 143. Thevalve 145 controls flow of a pressure fluid in and out of a cylinder 147for producing a pressure fluid signal corresponding to the heatexpansion of the pipe 123 and thereby to the temperature of the reheatedmedium pressure steam. The thermostat connected to the pipe 129 is ofthe same type and produces a pressure fluid signal in a cylinder 148.The signals produced in the cylinders 147 and 148 are conducted throughpipes 151 and 152 to the sides of a piston 154 in a cylinder 153. Thepiston 154, is therefore, moved according to the difference between thetemperature of the low pressure steam in the pipe 129 and thetemperature of the medium pressure steam in the pipe 123. The movementsof the piston 154 are transmitted by a piston rod to the valve 118 forcontrolling the distribution of the steam from the pipe 115 into theheat exchanger 116 or through the bypass pipe 119 directly into thesecond medium pressure reheater 122. FIG. 5a is a cross section of thevalve 118 and is self-explanatory.

The signals produced in the cylinders 147 and 148 are also conductedthrough pipes 162 and 158, respectively, to a cylinder 155 in which theyact against a spring 164 on the lower sides of connected pistons 157 and156 so that the energies of the two signals are added. The movement ofthe double piston 156, 157 is transmitted by a piston rod to the burner108 for tilting the latter so that the flame in the combustion chamber107 is directed upward when the sum of the reheat temperatures is toosmall and vice versa.

The temperature of the live steam is measured by a conventional device167 for producing a control signal actuating by conventional means, notshown, a valve 166 interposed in a feedwater by-pass pipe 165. When thetemperature of the live steam is too high, water passed by the valve 166is injected into the second superheater 111. If the temperature isnormal or too low the valve 166 is closed.

FIG. 6 diagrammatically illustrates an automatic control for a reheaterarrangement as shown in FIG. 2. Steam exhausting from a high pressureturbine 113 is consecutively conducted through a heat exchanger 116a, afirst medium pressure reheater 114, either through a heat exchanger 116or directly to a second medium pressure reheater portion 122, dependingon the position of a valve 171, and into a medium pressure turbine 124.The steam exhausting from the latter is consecutively conducted throughthe heat exchanger 116, a first low pressure reheater portion 127,either through the reheater 116a or directly to a second low pressurereheater portion 128, deepnding on the position of a valve 172, andtherefrom into a low pressure turbine 131. The valves 171 and 172 areactuated by a common actuating means 200 including a lever 173 which isactuated by a piston 154 in a cylinder 153. The actuating means 200simultaneously opens one of the valves and closes the other of thevalves. The piston 154 is responsive to the difierence of thetemperatures of the reheated medium pressure and of the reheated lowpressure steam which temperatures are measured by devices like thoseshown in FIG. 5.

PEG. 7 shows a modified apparatus for actuating the Valves 171 and 172whereby, upon swinging of the lever 173 in clockwise direction, thevalve 171 is actuated against the action of a spring 201 while theposition of the valve 172 is not changed, a spring 202 pressing a valveactuating arm 174 against an abutment 175. Swinging of the lever 173 incounterclockwise direction causes actu ation of the arm 174 and of thevalve 172 against the action of the spring 202 while the spring 201moves an arm 176, actuating the valve 171, against an abutment 177.Movement of the lever 173 is transmitted to the arms 174 and 176 bymeans of a bar 178 having a hook at each end for engaging the arms 174and 176. Depending on the length of the bar 178 and the distance of itshooks, the valves 171 and 172 are actuated alternatingly, as shown inFIG. 7, or, if the bar is shorter than shown in FIG. 7, the valves aremoved simultaneously during a certain period of time or a certain extentof the swinging of the lever 173, or, as shown in FIG. 6, during theentire extent of swinging of the lever 173.

I claim:

Apparatus for reheating steam of different pressures, comprising areheater for each steam pressure, at least two indirect heat exchangers,each heat exchanger having a heat exchange surface, first conduit meansinterconnecting a relatively hot portion of a first of said reheatersand a first of said heat exchangers for conducting relatively hot steamalong one side the heat exchange surface of said first heat exchanger,second conduit means connected to the inlet portion of a second of saidreheaters and to said first heat exchanger for conducting relativelycool steam along the other side of the heat exchange surface of saidfirst heat exchanger, third conduit means interconnecting a relativelyhot portion of said second reheater and a second of said heat exchangersfor conducting relatively hot steam along one side of the heat exchangesurface of said second heat exchanger, fourth conduit means connected tothe inlet portion of said first reheater and to said second heatexchanger for conducting relatively cool steam along the other side ofthe heat exchange surface of said second heat exchanger, a valveinterposed in said first conduit means for, controlling the how ofrelatively hot steam to said first heat exchanger, a valve interposed insaid third conduit means for controlling the flow of relatively hotsteam to said second heat exchanger, and actuating means interconnectingsaid valves and including means for simultaneously opening one of saidvalves and closing the other of said valves and vice versa.

FOREIGN PATENTS German application 1029 388 printed May 8, 1958 (Kl. 14H4/01).

